This invention relates to a novel cationic copolymers which were obtained by graft-polymerizing an olefin monomer onto a cationic derivative of a water-soluble linear polymer having hydroxyl groups. Recently, the mechanism of the reaction between antigen and antibody has been studied and clinical tests have become easy to carry out by using the following L.A. reaction. Namely, a latex sensitized with an antibody or an antigen is agglutinated by an antigen or an antibody, and by using the phenomenon it can be confirmed rapidly whether the antigen or the antibody is in existence. The latex used for the L.A. (Latex Agglutination) test should be stable and a soapless pure substance desirably. It is shown in U.S. Pat. No. 3,989,656 that a dextran-alkyl methacrylate graft composition is obtained by polymerizing an olefin monomer onto a water-soluble linear polymer dextran in water using ceric ammonium nitrate.
The present invention provides a novel graft-copolymer which is composed of a cationic derivative of a water-soluble linear polymer and an olefin monomer. The present invention also provides a method of graft-polymerizing an olefin monomer onto the cationic derivative of a water-soluble linear polymer in water using ceric ammonium nitrate to get a stable and soapless latex of the graft-copolymer.